Electron Configuration
Orbitals
•
•
•
Remember that orbitals simply represent an area
where the electron is most likely to be found.
Formally, orbitals are defined using four quantum
numbers
Orbitals have particular shapes, and not all of them
are “spherical”.
• In chemistry, there are four common orbital
shapes known respectively as s, p, d, and f
orbitals.
• Each shape within an orbital can hold at most
two electrons
S-Orbitals
The s orbital has a
spherical shape
centered around
the origin of the
three axes in space.
Because there is
only one subshell
shape, s-orbitals
can only hold two
electrons
P-Orbitals
There exist three p-orbitals subshell shapes.
Each p-orbital falls along the x, y, and z-axis
respectively. With three subshell shapes, porbitals can hold 6 electrons
D-orbitals
There exist 5 subshell
shapes for d-orbitals,
which are shown to the
left. Four look like “double
dumbells” while a fifth has
a “doughnut”
With 5 shapes, d-orbitals
can hold 10 electrons
The Seven F-Orbitals (14 e-)
Electron Energy Levels (Shells)
Generally symbolized
by “n”, it denotes the
probable distance of
the electron from the
nucleus. “n” is also
known as the Principal
Quantum Number
Number of electrons
that can fit in a shell:
2n2
Electron Configuration
• Electron configuration is a way to indicate
where the electrons are located in an atom
• As each element has a distinct and unique
number of protons, each neutral atom (and
thus element) has a unique electron
configuration.
• You can think of electron configuration as an
“address” or “mailbox number” for any given
element on the periodic table
Electron Configuration
• Electrons fill an atom according to four
principles
• The Pauli Exclusion Principle
• States that each electron orbital can only hold two
electrons
• The Aufbau Principle
• Hund’s Rule
• The Electron Spin Rule
Aufbau Principle
• States electrons fill orbitals from the lowest
to the highest energy level
Suppose I
had 12
electrons.
How will
they fill the
shells?
First shell can
only hold 2
electrons (2n2 =
2) [n=1]
Second shell
can hold 8
electrons (2n2 =
8) [n=2]
Electron Spin
• Refers to the angular momentum (in other
words, the spin direction) of an electron
In chemistry, this is
written as…
Electron Spin Rule
• States that no two electrons of the same spin
can occupy the same orbital
Hund’s Rule
• States that electrons of the same spin must occupy all
suborbitals first.
• In other words, before orbitals can “fill up” with two
electrons, all suborbitals must have one.
Electron Configurations
• There are several steps to finding the electron
configuration of an element.
• Suppose we wanted to know the electron
configuration of Sodium.
• Step #1: Determine how many electrons are in the
element
• With Sodium, there are 11 electrons
Electron Configurations (Sodium)
• Step #2: Determine how the electrons fill the
available electron orbitals
This chart is known as the
diagonal method.
Electrons start filling in the 1s
orbital, then the 2s orbital, then
the 2p, 3s, 3p, 4s, etc.
Remember, each s orbital can
hold 2 electrons, p orbitals can
hold 6, d orbitals can hold 10,
and f orbitals can hold 14
Electron Configurations (Sodium)
• Step #2: Determine how the electrons fill the
available electron orbitals
• As Sodium has 11 electrons…
•The 1s orbital is completely filled
(2 electrons)
•The 2s orbital is filled (2
electrons)
•The 2p orbital is filled (6
electrons)
•There is one electron in the 3s
orbtial
Thus Sodium’s electron configuration
is: 1s22s22p63s1
Electron Configurations (Sodium)
• Step #2: Determine how the electrons fill the
available electron orbitals
1
Helium is
here!
2
1
2
3
4
5
6
7
8
1
9
2
3
4
5
6
Or…you can use the
periodic table to easily
figure out electron
configurations.
10
First, familiarize
yourself with the
modified table to the
left.
1
2
3
4
5
6
7
8
9
10
11
12 13
14
Electron Configurations (Sodium)
• Step #2: Determine how the electrons fill the
available electron orbitals
1
2
1
2
3
1
4
2
5
6
7
8
3
4
5
6
9
7
1
2
3
4
9
10
11
12 13
5
6
10
8
14
Now, identify where
on this table your
element is.
Electron Configurations (Sodium)
• Step #2: Determine how the electrons fill the
available electron orbitals
1
S-Block
2
D-Block
1
2
3
4
5
6
7
8
1
9
2
3
4
5
6
Next, identify the
block your element is
located in.
10
P-Block
1
2
3
4
5
6
7
8
9
10
11
12 13
14
F-Block
Electron Configurations (Sodium)
• Step #2: Determine how the electrons fill the
available electron orbitals
1
2
1
1
2
3
1
4
2
5
6
7
8
3
4
5
6
9
7
2
3
4
5
6
The format for the grid
is the period number,
followed by the block,
and finally the number
across the top as a
subscript
10
8
Write out the “grid
coordinates” that your
element is located in.
9
10
11
12 13
14
With Sodium, this
“grid coordinate”
would be 3s1
Electron Configurations (Sodium)
• Step #2: Determine how the electrons fill the
available electron orbitals
1
2
1
1
2
3
4
5
6
7
8
9
2
3
4
5
6
10
Next, write out from
left to right, top to
bottom, all the orbitals
that exist before
element’s grid
coordinate
So with Sodium, we
go through the 1s, 2s,
and 2p orbitals
1
2
3
4
5
6
7
8
9
10
11
12 13
14
Electron Configurations (Sodium)
• Next, write out your two “halves” next to each
other.
1s 2s 2p
All the orbitals
before the “grid
coordinate”
3s1
From the “grid
coordinate”
Electron Configurations (Sodium)
• Then with the orbitals before the grid coordinate,
add the number of electrons that can go into each
orbital (s=2, p=6, d=10, f=14)
1s22s22p6
These orbitals
are all filled!
3s1
From the “grid
coordinate”
Electron Configurations (Sodium)
• Finally, put both sides together to get the final
electron configuration
1s22s22p6 3s1
Electron Configurations (Sulfur)
• Sulfur has 16 electrons. So what would be its
electron configuration?
With 16 electrons, the 1s, 2s, 2p,
and 3s orbitals are completely
filled (2, 2, 6, 2 respectively)
The 3p orbital would have four
electrons
Therefore, Sulfur’s electron
configuration would be
1s22s22p63s23p4
Electron Configurations (Sulfur)
• Step #2: Determine how the electrons fill the
available electron orbitals
1
Sulfur ends with a 3p4
2
1
1
2
3
1
4
2
5
6
7
8
3
4
5
6
9
7
2
3
10
11
4
5
6
10
8
9
12 13
14
The orbitals in front of
Sulfur are 1s, 2s, 2p,
and 3s.
Electron Configurations (Sulfur)
• Place the two sides together,
1s 2s 2p 3s
These orbitals
are all filled!
3p4
From the “grid
coordinate”
Electron Configurations (Sulfur)
• Place the two sides together,
1s22s22p63s23p4
These orbitals
are all filled!
From the “grid
coordinate”
Electron Configurations (Copper)
• Copper has 29 electrons. So what would be its
electron configuration?
With 29 electrons, the 1s, 2s, 2p,
3s, 3p, and 4s orbitals are
completely filled (2, 2, 6, 2, 6, and
2 respectively)
The 3d orbital would have 9
electrons
Therefore, Copper’s electron
configuration would be
1s22s22p63s23p64s23d9
Electron Configurations (Copper)
• Step #2: Determine how the electrons fill the
available electron orbitals
1
2
1
1
2
3
1
4
2
5
6
7
8
3
4
5
6
9
7
2
3
4
5
6
The orbitals in front of
Copper are 1s, 2s, 2p,
3s, 3p, and 4s
10
8
Copper ends with a
3d9
9
10
11
12 13
14
Electron Configurations (Copper)
• Place the two sides together,
1s 2s 2p 3s 3p 4s
These orbitals
are all filled!
3d9
From the “grid
coordinate”
Electron Configurations (Copper)
• Place the two sides together,
1s22s22p63s23p64s2 3d9